In general, the formation of a fine pattern in the manufacturing process of semiconductor devices is carried out using photolithography. In addition, multiple substrates referred to as transfer masks are normally used to form this fine pattern. This transfer mask is typically provided with a fine pattern composed of a metal thin film and the like on a transparent glass substrate, and photolithography is also used to manufacture this transfer mask.
A mask blank having a thin film (such as a light shielding film) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate is used to manufacture a transfer mask by photolithography. The process used to manufacture a transfer mask using this mask blank includes an exposure step of drawing a desired pattern in a resist film formed on a mask blank, a development step of forming a resist pattern by developing the resist film in accordance with the desired pattern drawing, an etching step of etching the thin film in accordance with the resist pattern, and a step of stripping and removing the residual resist pattern. In the development step, a desired pattern is drawn (exposed) on a resist film formed on a mask blank. Next, a developing solution is supplied to the resist film to dissolve the site of the resist film that is soluble in the developing solution. As a result, a resist pattern is formed in the resist film. In the etching step, a site of the thin film where the resist pattern is not formed, namely a site where the thin film is exposed, is dissolved by dry etching or wet etching using this resist pattern as a mask. As a result, the desired mask pattern is formed on the transparent substrate. A transfer mask is obtained in this manner.
In miniaturizing the pattern of a semiconductor device, it is necessary to use a short wavelength for the wavelength of the exposure light source used in photolithography in addition to miniaturizing the pattern formed on the transfer mask. In recent years, increasingly shorter wavelengths are being used as indicated by the transition from KrF excimer lasers (wavelength: 248 nm) to ArF excimer lasers (wavelength: 193 nm) for use as the exposure light source during the manufacturing of semiconductor devices.
Binary masks having a light shielding pattern composed of a chromium-based material on a transparent substrate have conventionally been known to be used as transfer masks.
In recent years, binary masks for use with ArF excimer lasers have appeared that use a material containing a molybdenum silicide compound (MoSi-based material) for the light shielding film (Patent Literature 1). In addition, binary masks for use with ArF excimer lasers have also appeared that use a material containing a tantalum compound (tantalum-based material) for the light shielding film (Patent Literature 2). Patent Literature 3 describes that a light shielding film may be subjected to hydrogen embrittlement and deform in the case of cleaning a photomask composed of a light shielding film that uses a metal containing at least two of tantalum, niobium and vanadium by acid cleaning or with hydrogen plasma. It is also described that the solution thereof is to form a hydrogen blocking film that covers the upper surface and lateral surfaces of the light shielding film so as to be airtight after having formed a pattern in the light shielding film.
On the other hand, Patent Literature 4 describes a synthetic quartz glass substrate for use with an excimer laser and a method of manufacturing the same. Here, when the synthetic quartz glass is irradiated with excimer laser light, and particularly ArF excimer laser light, Si—O—Si bonds within the glass are cleaved by the high energy of the laser light, and as a result of the formation of paramagnetic defects referred to as E′ centers (E prime centers), an absorption region ends up forming in the 215 nm wavelength band, and as a result thereof, this was indicated to lead to a decrease in transmittance with respect to ArF excimer laser light. In addition, it is disclosed that, as a result of the concentration of hydrogen molecules in the synthetic quartz glass reaching a certain level or higher, the occurrence of paramagnetic defects can be reduced.